Currently, if a old label already containing a '/' (or a space) is edited, it is accepted,
but no new not allowed char can be added to the label.
(Previously, a sheet pin label was not filtered)
File "rules" has instructional text as comments near top.
2) Convert all text files in repo to LF line ending form.
Any checkout done with "rules" in play will convert the working
tree to native line ending, while keeping repo as LF line ending.